1. Field of the Invention
This invention relates to a field test kit and method of on-site testing for the presence of contaminants and chemicals and, more particularly, to a micro spot method for detecting the presence of a variety of chemicals and environmental contaminants.
2. Description of the Prior Art
In view of biological hazards associated with toxic chemicals and environmental contaminants, regulations have been established by legislatures and environmental agencies to monitor a wide variety of chemicals and their byproducts. As a result, it is often necessary to conduct on-site inspections and analyses of various chemical spills, dump sites, and manufacturing facilities to detect environmental contaminants, hazardous conditions and to assure compliance with environmental regulations
Advantages of on-site inspection and analysis of chemical sites include resolving ambiguities during the inspection, reducing the potential for contamination and cross-contamination of samples during travel to off-site testing laboratories, and providing a convenient method of performing a large number of preliminary tests to detect and screen for chemical contaminants. On-site inspection also provides a rapid indication of those samples which may possibly contain compounds that must be identified using more sophisticated laboratory analytical techniques. On-site testing also allows the level of concentration and spread of contamination from chemical spills to be readily surmised.
Reagent-based chemical detection and chromatographic methodologies are attractive for on-site testing and screening because many tests can be run in a short period of time and they are capable of providing visual presumptive evidence of the presence of a chemical substance in a sample. One methodology comprises classical spot tests that are normally carried out in depressions or wells of a porcelain spot plate. Conventionally, small amounts of a solution, which may contain chemical contaminants, are placed in the wells of the spot plate. Small quantities of different reagents are then added to the solution samples and a positive test is normally signified by a color change in the well of the spot plate. An advantage with these tests is that a number of tests can be carried out on a single plate. For example, as many as 12 different spot tests can be carried out on a small 3.5xc3x974.5 inch spot plate. Another advantage is that it is possible to rapidly screen a large number of samples during a short period of time. However, as the concentration of the chemical substances become more dilute, it becomes more difficult to reliably detect the presence of the chemical substances. In most cases, the lower limit of detection is in the 1-100 microgram range.
Another methodology for screening samples and detecting target analytes in samples involves the use of thin layer chromatography (or TLC), which conventionally utilizes a plate having a surface layer formed of a sorbent material or gel. In order to separate the components of the analyte obtained from a sample, a drop of solution is carefully applied above the bottom edge of a thin layer chromatography plate. Solutions suspected of containing target analytes are preferably deposited onto the surface of a TLC plate in the form of a drop to avoid a streaking pattern that would result if the device for applying the drop actually contacts the surface of the plate while a sample solution is being deposited. After the solvent evaporates, the residue on the plate is eluted with another solvent or solvent mixture (also known as the eluant) thereby causing the chemical components of the sample to migrate towards the top or opposite edge of the plate. When the proper conditions and eluant are chosen, each analyte migrates across the plate at a rate that is different from the other analytes. The elution step results in the different analytes separating from each other and settling at different regions as diffuse spots along the path of migration. After the elution step, the plates are allowed to dry and then they are sprayed with a solution of a visualization reagent (detector reagent). A persistent concern with thin layer chromatography is that the elution step of waiting for the solvent to completely wet the plate and for the analytes to migrate and separate is relatively time-consuming. In many instances, proper completion of the elution phase may exceed an hour and warrant involved techniques and quality control steps to assure adequate separation of the different analytes. Another concern involves situations where the analytes are present in such low concentrations that the detection signals obtained in the tests are weak and can possibly be misread. In summary, with thin layer chromatography the analytes in the sample migrate and separate into localized regions, as opposed to remaining concentrated at spots or points.
In testing a sample solution for the presence of an analyte, much effort is often expended in preparing the reagent solutions used to detect the analyte. In order to maximize shelf-life storage stability, the detector reagents required for the tests are stored in the dry state and preferably in an inert atmosphere. When a reagent solution is required, a predetermined amount of dry reagent is mixed with an appropriate solvent to form a reagent solution having a particular concentration. In conducting tests at field sites that are remote from a laboratory, the time required to prepare several reagent solutions, take precautions to avoid spillage and dispose of excess reagent solutions after completing the tests may exceed the time actually devoted to testing a sample solution for an analyte.
For various tests, reagents have been pre-deposited in suitable mediums. Litmus paper is an example. Other examples are disclosed in U.S. Pat. No. 4,301,027 assigned to Dynamit Nobel AG and a divisional patent, U.S. Pat. No. 4,436,823 assigned to Dragerwerk Aktiengesellschaft where silica gel materials incorporate insolubilized reagents for colorimetric testing. A further example is set forth in U.S. Pat. No. 5,308,495 where doped sol-gel glasses contain colorimetric reagents. A more recent example is set forth in U.S. Pat. No. 5,824,526, which discloses that sol-gel glass forms a solid support for reagents which are trapped therein. Examples of literature related to the use of dry reagents and chemical testing include: Dry Reagent Chemical Tests, Analytical Communications, 34, 1H-3H (1997) by T. E. Edmonds, J. M. Lee, and J. D. Lee; Solid Phase Chemistry: Its Principles And Applications In Clinical Analysis, Talanta 31, 863(1984) by A. Zipp and W. E. Hornby; Chemistry On A Stick (Part 1), Chemtech 21, 462 (1991) by E. Diebold, M. Rapkin and A. Usmami; and Chemistry On A Stick (Part 2), Chemtech 21, 547 (1991) by A. Burke, J. DuBois, A. Azhar and A. Usmani. To improve shelf-life stability of detector reagents predeposited on a test medium, such as a plate containing a chromatographic silica gel medium with different reagents pre-deposited in the silica gel, the test medium can be sealed, preferably in an inert atmosphere, to prevent oxidation, hydrolysis or other types of degradation of the dry detector reagents. This may include sealing the silica gel plates in a plastic bag under a vacuum and in an inert atmosphere, as discussed for example in U.S. Pat. No. 5,837,288.
Other disclosures generally related to dry reagent tests include U.S. Pat. Nos. 4,729,959, 4,755,472, 4,843,377, 5,190,863, 5,326,697, 5,330,715, 5,418,141, 5,498,547, 5,510,245, 5,610,072, 5,656,739, 5,739,305, 5,756,296, 5,801,061, 5,824,491, 5,846,754, 5,856,199, and 5,848,797.
The micro spot test system and methodology of the present invention relates to an apparatus and method for the testing of analytes contained in a sample by dissolving the analytes in a solvent and utilizing capillary deposition techniques to concentrate the analytes on sorbent materials. Detector reagents are pre-deposited on the sorbent materials to form different reaction sites or regions for receiving the solution containing the analytes. Detection sensitivity and accuracy for a range of concentrations of analytes is provided by applying by capillary deposition a solution containing the analytes to different regions of the sorbent layer that contain detector reagents so that the analytes in the solution become concentrated at the particular spot or point of deposition on the sorbent layer. The solutions are deposited by placing small diameter tubes containing the analyte solution in contact with the surface of the sorbent material so that the solutions are drawn from the small diameter tubes by capillary action. The detector reagents in the different reaction sites of the sorbent layer are pre-deposited on the sorbent to detect the presence of the analytes that are concentrated at the spot of the reaction sites where the small diameter tube contacts the sorbent layer.
A system for chromogenically detecting the presence of chemical analytes includes a means for obtaining a sample solution containing the analytes; a device for the capillary deposition of the sample solution; chromatographic sorbent materials; and chromogenic detector reagents which have been pre-deposited on the sorbent materials. Storage devices may be provided for the samples and for the sample solutions, capillary deposition devices, and the chromatographic sorbent materials containing the chromogenic detector reagents.
Accordingly, one object of the present invention is to provide a compact chemical screening apparatus which is of a self-contained, efficient design for rapid screening of solutions for the presence or absence of target analytes.
Another object of the present invention is to provide a chemical screening device which is relatively simple to use for sample solutions containing a wide range of analytes in a wide range of concentration levels.
These, together with still other objects of the invention, along with the various features which characterize the invention, are pointed out with particularity in the appended claims.